Spectral-Interference Wafer Thickness Meter

Principles

Dispersion unit

The infrared light of the wide wavelength band that has been
emitted from the SLD (Super Luminescent Diode), passes through the
sensor head via the polarization maintaining fiber optic cable, and
is then irradiated on the surface of the wafer. Once this is done,
some of the light is reflected and the remaining light passes
through the wafer and is then reflected by the reverse side.

2 reflected beams of light interfere with each other's wavelengths
and then return to the spectrum unit. The intensity of the
interference light is defined by the distance from the reference
surface to the target and it takes an extremely large value when
the distance is equal to an integral multiple of the wavelength.

Interference light is finely dispersed into individual wavelengths,
and the light intensity spectral distribution is acquired from the
CCD received light waveform. Additionally, wafer thickness is
calculated by performing wavelength analysis such as FFT.